Shim for a turbomachine blade

ABSTRACT

A shim ( 20 ) for a turbomachine blade ( 14 ), the shim comprising two branches ( 20 A) for coming against bearing surfaces ( 16 A) of the blade rotor ( 16 ), and a base part ( 20 B) interconnecting the branches. The shim presents, at least in its branches ( 20 A), a multilayer structure having at least three layers ( 31, 32, 33 ) that are fastened to one another and superposed in the following order: a first layer ( 31 ) of a first material; a second layer ( 32 ) of a second material; and a third layer ( 33 ) of a third material that is optionally different from the first material, said first and third materials presenting respective first and third Young&#39;s moduluses of values E and E′ at any arbitrary operating temperature in the operating temperature range of the shim, and said second material presenting a second Young&#39;s modulus of value lying in the range E/20 to E/5 and in the range E′/20 to E′/5 at said operating temperature.

The invention relates to shim for a turbomachine blade, the shim beingof the type comprising two branches that are to come against the bearingsurfaces of a blade root, together with a base part interconnecting thebranches.

BACKGROUND OF THE INVENTION

The shim can be used with any type of turbomachine whether terrestrialor for aviation purposes (turbojet, turboprop, terrestrial gas turbine,etc.). In the particular circumstance of a bypass, two-spool airplaneturbojet, the shim of the invention can be used for the fan blades, orfor the moving blades of the low pressure compressor (or “booster”), orfor the high pressure compressor, or for the high pressure turbine, orfor the low pressure turbine of the turbojet.

In the present application, the axial direction corresponds to thedirection of the axis A of the rotor of the turbomachine, and the radialdirection is a direction perpendicular to the axis A. Furthermore,unless specified to the contrary, adjectives such as “inner” and “outer”are used relative to a radial direction in such a manner that the(radially) inner portion of an element is closer to the axis A than isthe (radially) outer portion of the same element.

In a rotor disk (i.e. a disk secured to the rotor) of a turbomachine,that serves to carry blades, the (moving) blades are fastened to thedisk by attachment systems, which may be constituted by shank-typefasteners that may be rectilinear or curvilinear, hammerhead-shaped, orChristmas-tree-shaped. Such fastener systems can be described as devicesin which the blade roots form the male portions of the system and areheld radially in the female portions of the system that are formed inthe outer periphery of the disk and that are commonly known as “slots”.

When the rotor is set into rotation, the blades are subjected mainly tocentrifugal forces and also to axial aerodynamic forces, and the bladeroots are pressed in abutment against portions of the disk lying oneither side of the outer opening of each slot, under the effect ofcentrifugal forces. The surfaces of the blade roots and of the disksthat come into abutment against each other are commonly referred to as“bearing surfaces”. These bearing surfaces are subjected to pressure (asa result of said forces applied to said bearing surfaces). To a firstapproximation, it can be estimated that this pressure depends on thesquare of the speed of rotation of the rotor.

It can thus be understood that the variations in the speed of rotationof the rotor during an operating cycle of the turbomachine: fromstationary to full throttle, passing through various particularintermediate speeds (idling, taxiing, cruising, descending, for anaviation turbomachine) give rise to variations in the pressure acting onthe above-defined bearing surfaces. These pressure variations associatedwith elastic deformations of the contacting parts give rise to relativemovements between the blade roots and the disk. When they are repeated,these relative movements, known as slip or as separation depending ontheir nature, give rise to wear phenomena in the bearing surfaces of theblades or of the disks. It is also possible for the dynamic movements ofthe blades at a given speed of rotation (response of the blades toalternating stresses of harmonic or transient nature) to contribute tothe phenomenon of said bearing surfaces becoming worn. These wearphenomena are naturally penalizing on the lifetime of a turbomachine.

Various so-called “anti-wear” solutions can be adopted, i.e. solutionsthat slow down the appearance of wear at the contact interfaces, andthese solutions include those based on inserting a third body, referredto as “shim”, between the blade roots and the disk. The shim serves inparticular to double the number of contact interfaces (going from asingle blade/disk interface to a pair of interfaces, blade/shim andshim/disk), and to reduce the relative movements between the parts thatare in contact, thus enabling wear to be reduced in operation.

A known example of shim of the above-mentioned type is described indocument FR 2 890 684. That shim is made entirely out of metal, and itis constituted by a sheet of metal that is folded appropriately.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a shim that is more effectivethan the above-mentioned known shim in terms of performing the“anti-wear” function, so as to provide better protection to the bearingsurfaces of the blades and of the disk.

This object is achieved by a shim for a turbomachine blade, the shimcomprising two branches for coming against bearing surfaces of the bladerotor, and a base part interconnecting the branches, the shim beingcharacterized in that it presents, at least in its branches, amultilayer structure having at least three layers that are fastened toone another and superposed in the following order: a first layer of afirst material; a second layer of a second material; and a third layerof a third material that is optionally different from the firstmaterial, said first and third materials presenting respective first andthird Young's moduluses of values E and E′ at any arbitrary operatingtemperature in the operating temperature range of the shim, and saidsecond material presenting a second Young's modulus of value lying inthe range E/20 to E/5 and in the range E′/20 to E′/5 at said operatingtemperature.

It should be noted that the Young's modulus of a material varies as afunction of the temperature of the material, and consequently that thevalues E and E′ depend on temperature.

The term “operating temperature” is used to mean the temperature towhich the shim is subjected while the turbomachine is in operation undernormal conditions of use. In the present invention, the relationshipbetween said first, second, and third Young's moduluses, as definedabove, needs to be satisfied for all of the temperatures in the range ofoperating temperatures of the shim.

For example, when the shim belongs to the fan or to the low pressurecompressor of a bypass two-spool airplane turbojet, its operatingtemperature lies in the range 20° C. to 150° C. When it belongs to thehigh pressure compressor of a bypass two-spool airplane turbojet, itsoperating temperature lies in the range 150° C. to 500° C. When itbelongs to the high pressure turbine of a bypass two-spool airplaneturbojet, its operating temperature lies in the range 400° C. to 700° C.

The present invention thus relates to adopting said multilayer structurein which the (isotropic or anisotropic) elasticity characteristics ofthe second material are better than the (isotropic or anisotropic)elasticity characteristics of the first and third materials in thedesired operating temperature range.

In an embodiment, said first and third materials are the same ordifferent metal alloys or organic matrix composite materials, while saidsecond material is non-metallic. For example, and in non-exhaustivemanner, the second material may be made of rubber, of silicone, ofpolyimide, of glass, or of epoxy resin.

The multilayer structure of the shim of the invention has the followingeffects:

-   -   uniformly distributing contact pressures by accommodation of the        shim as a result of the elasticity of the second layer;    -   on a change in speed of rotation, limiting relative movements        between parts due to centrifugal forces by virtue of “static”        shear in the second layer; and    -   damping any dynamic movements of the blade by “dynamic” shear of        the second layer.

A particular consequence of these effects is to prevent or limit wearphenomena in the bearing surfaces, thereby increasing the lifetimes ofblade roots and of disks.

These effects are reinforced when the second material presentsviscoelastic behavior in the operating temperature range of the shim,more particularly for the purpose of damping any dynamic movements ofthe blade.

The invention also provides a turbomachine rotor assembly comprising: arotor disk presenting slots in its outer periphery; blades fastened viatheir roots in said slots; and shims according to the invention, eachbranch of each shim being disposed between the bearing surface of ablade root and the corresponding bearing surface of the disk.

Finally, the invention also provides a turbomachine including such arotor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages can be better understood on reading thefollowing detailed description. The description refers to theaccompanying figures, in which:

FIG. 1 is a fragmentary exploded and diagrammatic view of a turbomachinerotor assembly comprising a rotor disk, an example of shim of theinvention, and a blade root;

FIG. 2 is a radial section view on plane II-II showing the FIG. 1assembly once it has been assembled;

FIG. 3 is a section view analogous to that of FIG. 2, showing anotherexample of shim of the invention; and

FIG. 4 is a section view analogous to that of FIG. 2, showing anotherexample of shim of the invention, placed between two adjacent slots.

MORE DETAILED DESCRIPTION

FIGS. 1 and 2 show: a rotor disk 2 having numerous grooves or “slots” 4in its periphery that define housings, each suitable for receiving theroot 16 of a blade 14, the root 16 being surrounded by a shim 20. Theblade root 16 and the fan disk 2 are made out of titanium alloy, forexample.

It should be observed that assemblies also exist (not shown) that have aspacer placed between the blade root 16 and the bottom of the slot 4.

When the disk 2 is set into rotation, the blades 14 are subjected tocentrifugal forces, and the bearing surfaces 16A on the blade root 16become pressed against bearing surfaces 22A of the disk 2. In theexample shown, the surfaces 16A constitute the flanks of the blade root16, while the surfaces 22A constitute the bottom faces of the lip-shapedportions 22 of the disk that extend on either side of the outer openingof each slot 4.

The shim 20 comprises two side branches 20A for coming against thebearing surfaces 16A of the blade root 16, and a base part 20B, here abase plate, interconnecting the branches and extending under the bladeroot 16. The shim 20 constitutes a wear piece and its main function isto limit wear of the blade root 16 and of the fan disk 2.

In the example of FIG. 2, the shim 20 presents a multilayer structure inits branches 20A and its base part 20B, which structure comprises threelayers 31, 32, 33 that adhere to one another. These three layers aresuperposed in the following order going from the blade root 16 towardsthe disk 2: a first layer 31 of a first material; a second layer 32 of asecond material; and a third layer 33 of a third material. In thisexample, the third material is identical to the first material, so thatthey present the same first Young's modulus. In accordance with theinvention, at any operating temperature T of the shim, the first Young'smodulus has a corresponding value E, and at said temperature T, saidsecond material presents a second Young's modulus with a value lying inthe range E/20 to E/5.

It should be observed that the shim 20 must present a certain amount ofstiffness in order to perform its mechanical function and its anti-wearfunction, such that the value of E is preferably greater than or equalto 110,000 megapascals (MPa) for metal shim (e.g. 210,000 MPa for shimmade of a nickel-based superalloy, of the type sold under the name“Inconel”), and greater than or equal to 70,000 MPa for shim made oforganic matrix composite material.

So far as the choice of materials is concerned, it naturally depends onthe operating temperature of the shim.

When the rotor assembly belongs to the fan or the low pressurecompressor of a bypass two-spool airplane turbojet, it is subjected tooperating temperatures lying in the range 20° C. to 150° C. Under suchcircumstances, and by way of example, it is possible for the firstmaterial to be selected as a Ni-based superalloy with more than 15% byweight Fe and Cr, such as the superalloy sold under the name “Inconel718”; while the second material can be rubber (natural or synthetic). Inthese circumstances, it is also possible for the first material to be acomposite material using an epoxy resin matrix with reinforcing fibers,e.g. made of carbon; the second material could then be an epoxy resin onits own (with the difference in Young's modulus between the first andsecond materials being associated with the absence of fibers).

When the assembly belongs to the high pressure compressor of a bypasstwo-spool airplane turbojet, it is subjected to operating temperatureslying in the range 150° C. to 500° C. Under such circumstances, and byway of example, it is possible to select for the first material aNi-based superalloy having more than 15% by weight of Fe and Cr, such asthe superalloy sold under the name “Inconel 718”; the second materialcould be a silicone or polyimide.

When the assembly belongs to the high pressure turbine of a bypasstwo-spool airplane turbojet, it is subjected to operating temperatureslying in the range 400° C. to 700° C. Under such circumstances, and byway of example, it is possible for the first material to be selected asan Ni-based superalloy with more than 15% by weight Fe and Cr, such asthe superalloy sold under the name “Inconel 718”; the second materialmay be glass (which in this operating temperature range presentsviscoelastic behavior).

In general, it should be observed that said layers 31, 32, 33 can befastened to one another in various ways, and in particular:

-   -   by natural adhesion when polymerizing the second layer 32 (or        when vulcanizing it if is made of rubber);    -   by adhesive;    -   by welding the layers 31 and 33 together in part and then        polishing them;    -   by brazing the layers 31 and 33 together in part, and then        polishing them;    -   by crimping; or    -   by combining the above techniques (e.g. natural adhesion and        crimping).

Said layers may be integral with one another to form said multilayerstructure, and the fastening that is obtained must naturally besufficiently secure to prevent the structure becoming delaminated inoperation and to prevent the layer 32 from creeping.

FIG. 3 is a section view analogous to that of FIG. 2 showing anotherelement of a shim 120 of the invention. Elements or element portionsthat are analogous between FIGS. 2 and 3 are identified by the samereference numerals plus 100.

The example of FIG. 3 differs from that of FIG. 2 in that the base part120B of the shim 120 is formed by the first and second layers 131 and133 joined to each other. Only the branches 120A of the shim present amultilayer structure made up of the first, second, and third layers 131,132, and 133 of the invention. It should be observed that the base part120B of the shim could also be formed solely by the third layer 133, orindeed solely by the first layer 131.

FIG. 4 is a section view analogous to that of FIG. 2 showing anotherexample of a shim 220 of the invention. Elements or element portionsanalogous between FIGS. 2 and 4 are identified with the same numericalreferences plus 200.

The example of FIG. 4 differs from that of FIG. 2 in that the base part220B of the shim 220 extends over the outer periphery of the rotor disk202 between two adjacent slots 204, with each branch 220A of the shimpenetrating into a slot 204 and being housed between the bearing surface216A of the blade root 216 and the corresponding bearing surface 222A ofthe disk 202.

The shim 220 presents a multilayer structure analogous to that of theshim 20 in FIG. 2, having three layers 231, 232, 233 that are fastenedto one another and superposed.

1. A shim for a turbomachine blade, the shim comprising two branches forcoming against bearing surfaces of the blade rotor, and a base partinterconnecting the branches, the shim presenting, at least in itsbranches, a multilayer structure having at least three layers that arefastened to one another and superposed in the following order: a firstlayer of a first material; a second layer of a second material; and athird layer of a third material that is optionally different from thefirst material, said first and third materials presenting respectivefirst and third Young's moduluses of values E and E′ at any arbitraryoperating temperature in the operating temperature range of the shim,and said second material presenting a second Young's modulus of valuelying in the range E/20 to E/5 and in the range E′/20 to E′/5 at saidoperating temperature.
 2. A shim according to claim 1, in which saidfirst and third materials are identical.
 3. A shim according to claim 1,in which said first and third materials are metal alloys or organicmatrix composite materials, while the second material is non-metallic.4. A shim according to claims 1, in which said second material presentsviscoelastic behavior in the operating temperature range of the shim. 5.A shim according to claim 1, in which said first, second, and thirdlayers also extend in the base part of the shim.
 6. A turbomachine rotorassembly comprising: a rotor disk presenting slots in its outerperiphery; blades fastened by their roots in said slots; and shimsaccording to any preceding claim, each branch of each shim beingdisposed between the bearing surface of a blade root and thecorresponding bearing surface of the disk.
 7. A turbomachine rotorassembly according to claim 6, in which the base part of each shimextends under each blade root.
 8. A turbomachine rotor assemblyaccording to claim 6, in which the base part of each shim extends overthe outer periphery of the disk, between two adjacent slots.
 9. Aturbomachine comprising a rotor assembly according to claim 6.